Nitric oxide and the vascular endothelium in myocardial ischemia-reperfusion injury

S-Nitroso Human Serum Albumin Enhances Left Ventricle Hemodynamic Performance and Reduces Myocardial Damage after Local Ischemia-Reperfusion Injury

Endothelial nitric oxide (NO) production is crucial in maintaining vascular homeostasis. However, in the context of ischemia-reperfusion (I/R) injury, uncoupled endothelial nitric oxide synthase (eNOS) can exacerbate reactive oxygen species (ROS) generation. Supplementation with S-nitroso human serum albumin (S-NO-HSA) offers a potential solution by mitigating eNOS uncoupling, thereby enhancing NO bioavailability. In a study conducted at the University of Verona, male rats underwent thoracotomy followed by 30 min left anterior descendant coronary (LAD) occlusion and subsequent reperfusion. Hemodynamic parameters were meticulously assessed using a conductance catheter inserted via the carotid artery. The rats were stratified into two main groups based on reperfusion duration and the timing of drug infusion, with the effects of S-NO-HSA evaluated after 2 or 24 h. Remarkably, intravenous administration of S-NO-HSA, initiated before or during ischemia, exhibited notable benefits. It significantly improved left ventricular function, safeguarded energetic substrates such as phosphocreatine and ATP, and sustained glutathione levels akin to basal conditions, indicative of diminished oxidative stress. The data from this study strongly suggest a protective role for S-NO-HSA in mitigating I/R injury induced by LAD artery occlusion, a phenomenon observed at both 2 and 24 h post-reperfusion. These findings underscore the promising therapeutic potential of NO supplementation in alleviating myocardial damage subsequent to ischemic insult.

Effects of graft preservation conditions on coronary endothelium and cardiac functional recovery in a rat model of donation after circulatory death

BACKGROUND

Use of cardiac grafts obtained with donation after circulatory death (DCD) could significantly improve donor heart availability. As DCD hearts undergo potentially deleterious warm ischemia and reperfusion, clinical protocols require optimization to ensure graft quality. Thus, we investigated effects of alternative preservation conditions on endothelial and/or vascular and contractile function in comparison with the current clinical standard.

METHODS

Using a rat DCD model, we compared currently used graft preservation conditions, St. Thomas n°2 (St. T) at 4°C, with potentially more suitable conditions for DCD hearts, adenosine-lidocaine preservation solution (A-L) at 4°C or 22°C. Following general anesthesia and diaphragm transection, hearts underwent either 0 or 18 min of in-situ warm ischemia, were explanted, flushed and stored for 15 min with either St. T at 4°C or A-L at 4°C or 22°C, and then reperfused under normothermic, aerobic conditions. Endothelial integrity and contractile function were determined.

RESULTS

Compared to 4°C preservation, 22°C A-L significantly increased endothelial nitric oxide synthase (eNOS) dimerization and reduced oxidative tissue damage (p < 0.05 for all). Furthermore, A-L at 22°C better preserved the endothelial glycocalyx and coronary flow compared with St. T, tended to reduce tissue calcium overload, and stimulated pro-survival signaling. No significant differences were observed in cardiac function among ischemic groups.

CONCLUSIONS

Twenty-two-degree Celsius A-L solution better preserves the coronary endothelium compared to 4°C St. T, which likely results from greater eNOS dimerization, reduced oxidative stress, and activation of the reperfusion injury salvage kinase (RISK) pathway. Improving heart preservation conditions immediately following warm ischemia constitutes a promising approach for the optimization of clinical protocols in DCD heart transplantation.

Oral pre-treatment with thiocyanate (SCN-) protects against myocardial ischaemia-reperfusion injury in rats

Despite improvements in revascularization after a myocardial infarction, coronary disease remains a major contributor to global mortality. Neutrophil infiltration and activation contributes to tissue damage, via the release of myeloperoxidase (MPO) and formation of the damaging oxidant hypochlorous acid. We hypothesized that elevation of thiocyanate ions (SCN⁻), a competitive MPO substrate, would modulate tissue damage. Oral dosing of rats with SCN⁻, before acute ischemia–reperfusion injury (30 min occlusion, 24 h or 4 week recovery), significantly reduced the infarct size as a percentage of the total reperfused area (54% versus 74%), and increased the salvageable area (46% versus 26%) as determined by MRI imaging. No difference was observed in fractional shortening, but supplementation resulted in both left-ventricle end diastolic and left-ventricle end systolic areas returning to control levels, as determined by echocardiography. Supplementation also decreased antibody recognition of HOCl-damaged myocardial proteins. SCN⁻ supplementation did not modulate serum markers of damage/inflammation (ANP, BNP, galectin-3, CRP), but returned metabolomic abnormalities (reductions in histidine, creatine and leucine by 0.83-, 0.84- and 0.89-fold, respectively), determined by NMR, to control levels. These data indicate that elevated levels of the MPO substrate SCN⁻, which can be readily modulated by dietary means, can protect against acute ischemia–reperfusion injury.

Hypoxic preconditioning attenuates ischemia-reperfusion injury in young healthy adults

Ischemia-reperfusion injury induced by restoration of blood flow following occlusion impairs flow-mediated dilation, a marker of endothelium-dependent vasodilation. In young healthy adults, exposure to intermittent hypoxia, consisting of alternating short bouts of breathing hypoxic and normoxic air, before an ischemia-reperfusion injury significantly attenuated the reduction in flow-mediated dilation. Thus, hypoxic preconditioning represents a potential strategy to mitigate the effect of ischemia-reperfusion injury associated with ischemic events.

KRT1 gene silencing ameliorates myocardial ischemia-reperfusion injury via the activation of the Notch signaling pathway in mouse models

Myocardial ischemia and reperfusion injury (MIRI) includes major drawbacks, such as excessive formation of free radicals and also overload of calcium, which lead to cell death, tissue scarring, and remodeling. The current study aims to explore whether KRT1 silencing may ameliorate MIRI via the Notch signaling pathway in mouse models. Myocardial tissues were used for the determination of the positive rate of KRT1 protein expression, apoptosis of myocardial cells, creatine kinase (CK) and lactate dehydrogenase (LDH) expression, expression of related biomarkers as well as myocardial infarction area. The transfected myocardial cells were treated with KRT1-siRNA, Jagged1, and DAPT (inhibitor of Notch-1 signaling pathway). The expression of KRT1, NICD, Hes1, Bcl-2, and Bax protein was detected. The MTT assay was applied for cell proliferation and flow cytometry was used for cell apoptosis. Mice with MIRI had a higher positive rate of KRT1 protein expression, apoptosis of myocardial cells, CK and LDH expression, myocardial infarction area, increased expression of MDA, NO, SDH, IL-1, IL-6, TNF-α, CRP, KRT1, Bax protein, CK, and LDH, and decreased expression of SOD, NICD, Hes1, and Bcl-2. The downregulation of KRT1 led to decreased expression of KRT1 and Bax protein, increased expression of NICD, Hes1, and Bcl-2, decreased cell apoptosis, and improved cell proliferation. The inhibition of the Notch signaling pathway leads to reduced expression of Bax, increased expression of NICD, Hes1, and Bcl 2, and also decreased cell apoptosis and increased cell proliferation. Our data conclude that KRT1 silencing is able to make MIRI better by activating the Notch signaling pathway in mice.

Nitric oxide, PKC-ε, and connexin43 are crucial for ischemic preconditioning-induced chemical gap junction uncoupling

Ischemic preconditioning (IPC) maintains connexin43 (Cx43) phosphorylation and reduces chemical gap junction (GJ) coupling in cardiomyocytes to protect against ischemic damage. However, the signal transduction pathways underlying these effects are not fully understood. Here, we investigated whether nitric oxide (NO) and protein kinase C-ε (PKC-ε) contribute to IPC-induced cardioprotection by maintaining Cx43 phosphorylation and inhibiting chemical GJ coupling. IPC reduced ischemia-induced myocardial infarction and increased cardiomyocyte survival; phosphorylated Cx43, eNOS, and PKC-ε levels; and chemical GJ uncoupling. Administration of the NO donor SNAP mimicked the effects of IPC both in vivo and in vitro, maintaining Cx43 phosphorylation, promoting chemical GJ uncoupling, and reducing myocardial infarction. Preincubation with the NO synthase inhibitor L-NAME or PKC-ε translocation inhibitory peptide (PKC-ε-TIP) abolished these effects of IPC. Additionally, by inducing NO production, IPC induced translocation of PKC-ε, but not PKC-δ, from the cytosolic to the membrane fraction in primary cardiac myocytes. IPC-induced cardioprotection thus involves increased NO production, PKC-ε translocation, Cx43 phosphorylation, and chemical GJ uncoupling.

Scutellarin's Cardiovascular Endothelium Protective Mechanism: Important Role of PKG-Iα

Scutellarin (SCU), a flavonoid glycoside compound, has been successfully used in clinic for treatment of ischemic diseases in China. In this report, we checked the effects of SCU on endothelium dysfunction (ED) of coronary artery (CA) against myocardial ischemia reperfusion (MIR) injury in vivo. The involvement of PKG-Iα was further studied using cultured endothelial cells subjected to hypoxia reoxygenation (HR) injury in vitro. In rat MIR model, SCU (45 and 90 mg/kg, iv) significantly reduced ischemic size and restored the endothelium-dependent vasodilation of isolated CA rings. PKG inhibitor Rp-8-Br-cGMP (50 μg/kg, iv) could ameliorate the protective effects of SCU. Increase in phosphorylation of vasodilator-stimulated phosphoprotein (VASP), a main substrate of PKG, at Ser 239 was observed in both heart tissue and serum of SCU-treated animals. In cultured human cardiac microvascular endothelial cells (HCMECs), SCU (1 and 10 μM) dose-dependently protected cell viability and increased the mRNA and protein level of PKG-Iα against HR injury. The activity of PKG was also increased by SCU treatment. The activation of PKG–1α was then studied using targeted proteomic analysis (MRM-MS) checking the phosphorylation state of the autophosphorylation domain (aa42-94). Significant decrease in phosphorylation of PKG-Iα at Ser50, Ser72, Ser89 was induced by HR injury while SCU treatment significantly increased the phosphorylation of PKG-Iα, not only at Ser50, Ser72 and Ser89, but also at Ser44 and Thr58 (two novel phosphorylation domains). Our results demonstrate PKG-Iα might play an important role in the protective effects of SCU on ED against MIR injury.

Scuba diving induces nitric oxide synthesis and the expression of inflammatory and regulatory genes of the immune response in neutrophils

OBJECTIVE

Scuba diving, characterized by hyperoxia and hyperbaria, could increase reactive oxygen species production which acts as signaling molecules to induce adaptation against oxidative stress. The aim was to study the effects of scuba diving immersion on neutrophil inflammatory response, the induction of oxidative damage, and the NO synthesis.

DESIGN

Nine male divers performed a dive at 50 m depth for a total time of 35 min. Blood samples were obtained at rest before the dive, after the dive, and 3 h after the diving session.

MEASUREMENTS

Markers of oxidative and nitrosative damage, nitrite, and the gene expression of genes related with the synthesis of nitric oxide and lipid mediators, cytokine synthesis, and inflammation were determined in neutrophils.

RESULTS

The mRNA levels of genes related with the inflammatory and immune response of neutrophils, except TNF-α, myeloperoxidase, and toll-like receptor (TLR) 2, significantly increased after the recovery period respect to predive and postdive levels. NF-κB, IL-6, and TLR4 gene expression reported significant differences immediately after diving respect to the predive values. Protein nitrotyrosine levels significantly rose after diving and remained high during recovery, whereas no significant differences were reported in malondialdehyde. Neutrophil nitrite levels as indicative of inducible nitric oxide synthase (iNOS) activity progressively increased after diving and recovery. The iNOS protein levels maintained the basal values in all situations.

CONCLUSION

Scuba diving which combines hyperoxia, hyperbaria, and acute exercise induces nitrosative damage with increased nitrotyrosine levels and an inflammatory response in neutrophils.

Arginase regulates red blood cell nitric oxide synthase and export of cardioprotective nitric oxide bioactivity

The theory that red blood cells (RBCs) generate and release nitric oxide (NO)-like bioactivity has gained considerable interest. However, it remains unclear whether it can be produced by endothelial NO synthase (eNOS), which is present in RBCs, and whether NO can escape scavenging by hemoglobin. The aim of this study was to test the hypothesis that arginase reciprocally controls NO formation in RBCs by competition with eNOS for their common substrate arginine and that RBC-derived NO is functionally active following arginase blockade. We show that rodent and human RBCs contain functional arginase 1 and that pharmacological inhibition of arginase increases export of eNOS-derived nitrogen oxides from RBCs under basal conditions. The functional importance was tested in an ex vivo model of myocardial ischemia-reperfusion injury. Inhibitors of arginase significantly improved postischemic functional recovery in rat hearts if administered in whole blood or with RBCs in plasma. By contrast, arginase inhibition did not improve postischemic recovery when administered with buffer solution or plasma alone. The protective effect of arginase inhibition was lost in the presence of a NOS inhibitor. Moreover, hearts from eNOS(-/-) mice were protected when the arginase inhibitor was given with blood from wild-type donors. In contrast, when hearts from wild-type mice were given blood from eNOS(-/-) mice, the arginase inhibitor failed to protect against ischemia-reperfusion. These results strongly support the notion that RBCs contain functional eNOS and release NO-like bioactivity. This process is under tight control by arginase 1 and is of functional importance during ischemia-reperfusion.

Daily ischemic preconditioning provides sustained protection from ischemia-reperfusion induced endothelial dysfunction: a human study

Background

It is well established that acute ischemic preconditioning (IPC) protects against ischemia–reperfusion (IR) injury; however, the effectiveness of repeated IPC exposure has not been extensively investigated. We aimed to determine whether daily IPC episodes provide continued protection from IR injury in a human forearm model, and the role of cyclooxygenase‐2 in these responses.

Methods and Results

Thirty healthy volunteers were randomized to participate in 2 of 3 protocols (IR alone, 1‐day IPC, 7‐day IPC) in an operator‐blinded, crossover design. Subjects in the IR alone protocol underwent flow‐mediated dilation (FMD) measurements pre‐ and post‐IR (15′ upper‐arm ischemia and 15′ reperfusion). The 1‐day IPC protocol involved FMD measurements before and after 1 episode of IPC (3 cycles of 5′ upper‐arm ischemia and 5′ reperfusion) and IR. Day 7 of the 7‐day IPC protocol was identical to the 1‐day IPC protocol but was preceded by single daily episodes of IPC for 6 days prior. During each protocol, subjects received a 7‐day treatment of either the cyclooxygenase‐2 inhibitor celecoxib or placebo. Pre‐IR FMD was similar between groups. IR alone reduced FMD post‐IR (placebo, ΔFMD: −4.4±0.7%; celecoxib, ΔFMD: −5.0±0.5%). One‐day IPC completely prevented this effect (placebo, ΔFMD: −1.1±0.6%; celecoxib, ΔFMD: 0.0±0.7%; P<0.0001). Similarly, 7‐day IPC demonstrated persistent endothelial protection post‐IR (placebo, ΔFMD: −0.9±0.9%; celecoxib, ΔFMD: 0.0±0.8%; P<0.0001, P<0.0001 for ANOVA effect of IPC protocol). Celecoxib did not alter responses to IR in any protocol.

Conclusions

Daily episodes of IPC provide sustained protection from IR‐induced endothelial dysfunction in humans through a mechanism that appears cyclooxygenase‐2‐independent.

Review of inhaled nitric oxide in the pediatric cardiac surgery setting

Surgical intervention for congenital heart disease (CHD) can be complicated by pulmonary hypertension (PH), which increases morbidity, mortality, and medical burden. Consequently, postoperative management of PH is an important clinical consideration to improve outcomes. Inhaled nitric oxide (iNO) is a widely accepted standard of care for PH and has been studied in the context of cardiac surgery for CHD. However, large randomized, double-blind, placebo-controlled, multicenter clinical trials in pediatric patients are limited. This review will provide an overview of the clinical studies in this setting and will discuss general treatment considerations to facilitate a better understanding of the clinical use of iNO for PH after pediatric cardiac surgery.

Role of Endothelial Cells in Myocardial Ischemia-Reperfusion Injury

Minimizing myocardial ischemia-reperfusion injury has broad clinical implications and is a critical mediator of cardiac surgical outcomes. “Ischemic injury” results from a restriction in blood supply leading to a mismatch between oxygen supply and demand of a sufficient intensity and/or duration that leads to cell necrosis, whereas ischemia-reperfusion injury occurs when blood supply is restored after a period of ischemia and is usually associated with apoptosis (i.e. programmed cell death). Compared to vascular endothelial cells, cardiac myocytes are more sensitive to ischemic injury and have received the most attention in preventing myocardial ischemia-reperfusion injury. Many comprehensive reviews exist on various aspects of myocardial ischemia-reperfusion injury. The purpose of this review is to examine the role of vascular endothelial cells in myocardial ischemia-reperfusion injury, and to stimulate further research in this exciting and clinically relevant area. Two specific areas that are addressed include: 1) data suggesting that coronary endothelial cells are critical mediators of myocardial dysfunction after ischemia-reperfusion injury; and 2) the involvement of the mitochondrial permeability transition pore in endothelial cell death as a result of an ischemia-reperfusion insult. Elucidating the cellular signaling pathway(s) that leads to endothelial cell injury and/or death in response to ischemia-reperfusion is a key component to developing clinically applicable strategies that might minimize myocardial ischemia-reperfusion injury.

Vasculoprotective Effects of Apolipoprotein Mimetic Peptides: An Evolving Paradigm In Hdl Therapy (Vascular Disease Prevention, In Press.)

Anti-atherogenic effects of high density lipoprotein (HDL) and its major protein component apolipoprotein A-I (apoA-I) are principally thought to be due to their ability to mediate reverse cholesterol transport. These agents also possess anti-oxidant properties that prevent the oxidative modification of low density lipoprotein (LDL) and anti-inflammatory properties that include inhibition of endothelial cell adhesion molecule expression. Results of the Framingham study revealed that a reduction in HDL levels is an independent risk factor for coronary artery disease (CAD). Accordingly, there has been considerable interest in developing new therapies that specifically elevate HDL cholesterol. However, recent evidence suggests that increasing circulating HDL cholesterol levels alone is not sufficient as a mode of HDL therapy. Rather, therapeutic approaches that increase the functional properties of HDL may be superior to simply raising the levels of HDL per se. Our laboratory has pioneered the development of synthetic, apolipoprotein mimetic peptides which are structurally and functionally similar to apoA-I but possess unique structural homology to the lipid-associating domains of apoA-I. The apoA-I mimetic peptide 4F inhibits atherogenic lesion formation in murine models of atherosclerosis. This effect is related to the ability of 4F to induce the formation of pre-β HDL particles that are enriched in apoA-I and paraoxonase. 4F also possesses anti-inflammatory and anti-oxidant properties that are independent of its effect on HDL quality per se. Recent studies suggest that 4F stimulates the expression of the antioxidant enzymes heme oxygenase and superoxide dismutase and inhibits superoxide anion formation in blood vessels of diabetic, hypercholesterolemic and sickle cell disease mice. The goal of this review is to discuss HDL-dependent and -independent mechanisms by which apoA-I mimetic peptides reduce vascular injury in experimental animal models.

Pioglitazone inhibits angiotensin II-induced senescence of endothelial progenitor cell

We investigated whether a peroxisome proliferator-activated receptor (PPAR) agonist would effect the angiotensin II (Ang II)-induced senescence of endothelial progenitor cells (EPCs). EPCs were isolated from peripheral blood and characterized. Both reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting were used to assess gp91phox expression and angiotensin type 1 receptor (AT1R) levels. Immunofluorescence of nitrotyrosine provided evidence of peroxynitrite formation. Our data indicate that Ang II increased the expression of gp91phox mRNA, which was significantly diminished by pioglitazone, a PPARgamma agonist. Western blotting revealed that Ang II stimulated an increase in the gp91phox protein, whereas co-treatment with pioglitazone significantly reduced this increase. In addition, pioglitazone also inhibited Ang II-induced peroxynitrite formation. Interestingly, pioglitazone decreased the expressions of AT1R mRNA and protein. The exposure of cultured EPCs to Ang II (100 nmol/L) significantly accelerated the rate of senescence compared to that of the control cells during 14 d in culture, as determined by acidic beta-galactosidase staining. Ang II-induced EPC senescence was significantly inhibited by co-treatment with pioglitazone. Because cellular senescence is critically influenced by telomerase, which elongates telomeres, we also measured telomerase activity by means of PCR-ELISA-based assay. The results showed that Ang II significantly diminished telomerase activity, and this effect was significantly abolished by co-treatment with pioglitazone. In conclusion, pioglitazone inhibited Ang II-induced senescence of EPCs via down-regulation of the expression of AT1R.

Caveolin and proteasome in tocotrienol mediated myocardial protection

The effect of different isomers of tocotrienol was tested on myocardial ischemia reperfusion injury. Although all of the tocotrienol isomers offered some degree of cardioprotection, gamma-tocotrienol was the most protective as evident from the result of myocardial apoptosis. To study the mechanism of tocotrienol mediated cardioprotection, we examined the interaction and/or translocation of different signaling components to caveolins and activity of proteasome. The results suggest that differential interaction of MAP kinases with caveolin 1/3 in conjuncture with proteasome stabilization play a unique role in tocotrienol mediated cardioprotection possibly by altering the availability of pro-survival and anti-survival proteins.

Intra-arterial vitamin C prevents endothelial dysfunction caused by ischemia-reperfusion

OBJECTIVE

Ischemia-reperfusion (IR) injury causes tissue injury and endothelial dysfunction. There is evidence that oxidative stress plays an important role.

METHODS

We tested if IR-induced endothelial dysfunction could be prevented by administration of the antioxidant vitamin C. Twenty-six healthy male subjects and eight male patients with peripheral arterial disease (PAD) were enrolled in this randomised placebo-controlled study. Forearm blood flow (FBF) measurements in response to the vasodilators acetylcholine (ACh; endothelium-dependent agonist) or nitroglycerin (NTG; endothelium-independent) were performed before and after forearm ischemia for 20 min. FBF responses were reassessed during reperfusion with intra-arterial co-administration of 24 mg/min vitamin C or placebo. In six volunteers responses to the NO-synthase inhibitor N-monomethyl-L-arginine (L-NMMA) were also assessed before and after ischemia with and without vitamin C.

RESULTS

ACh-induced vasodilation was blunted in subjects receiving placebo after reperfusion (p<0.05 versus baseline). Administration of vitamin C completely prevented impaired responsiveness. NTG-induced vasodilation was not affected by reperfusion or vitamin C. This finding was consistent in patients with PAD and impaired endothelial function, where local vitamin C infusion restored FBF reactivity to ACh before and after IR injury (p<0.05 versus baseline). Again, NTG-induced vasodilation was not affected. Blunted L-NMMA responses seen during reperfusion could be completely reversed by vitamin C.

CONCLUSIONS

Our data indicate that IR-induced vascular injury can be prevented by administration of antioxidants.

Caveolin and MAP kinase interaction in angiotensin II preconditioning of the myocardium

Angiotensin II (Ang II) has been found to exert preconditioning (PC)-like effect in mammalian hearts. The present investigation reported for the first time a unique mitogen activated protein (MAP) kinase signalling in Ang II PC of the heart involving lipid rafts, which generated a survival signal by differentially associating MAP kinases with caveolin. A group of rat hearts was treated with Ang II in the absence or presence of NADPH oxidase inhibitor, apocynin or a cell permeable reactive oxygen species (ROS) scavenger, N-acetyl-cysteine (NAC). Ang II pre-treatment improved post-ischaemic ventricular recovery, myocardial infraction and decreased the number of cardiomyocyte apoptosis indicating PC effect of Ang II. Both apocynin and NAC abolished the PC ability of Ang II. In Ang II treated heart, there was a decreased association of p38MAPKbeta & extracellular-signal regulated kinase (ERK) 1/ 2 (anti-death signalling component) with caveolin while there was an increased association of p38MAPKalpha & Jun N-terminal kinase (JNK) (death signalling component) indicating reduced amount of death signal components and increased amount of anti-death signalling components being available to the Ang II treated heart to generate a survival signal, which was reversed with NAC or apocynin. The survival signal was also demonstrated by increased phosphorylation of serine/threonine-protein kinase B (AKT) and enhanced induction of expression of Bcl-2 during Ang II PC and its reversal with NAC & apocynin treated heart.

Controlled reperfusion after hypothermic heart preservation inhibits mitochondrial permeability transition-pore opening and enhances functional recovery

We investigated whether low-pressure reperfusion may attenuate postischemic contractile dysfunction, limits necrosis and apoptosis after a prolonged hypothermic ischemia, and inhibits mitochondrial permeability transition-pore (MPTP) opening. Isolated rats hearts (n = 72) were exposed to 8 h of cold ischemia and assigned to the following groups: 1) reperfusion with low pressure (LP = 70 cmH(2)O) and 2) reperfusion with normal pressure (NP = 100 cmH(2)O). Cardiac function was assessed during reperfusion using the Langendorff model. Mitochondria were isolated, and the Ca(2+) resistance capacity (CRC) of the MPTP was determined. Malondialdehyde (MDA) production, caspase-3 activity, and cytochrome c were also assessed. We found that functional recovery was significantly improved in LP hearts with rate-pressure product averaging 30,380 +/- 1,757 vs. 18,000 +/- 1,599 mmHg/min in NP hearts (P < 0.01). Necrosis, measured by triphenyltetrazolium chloride staining and creatine kinase leakage, was significantly reduced in LP hearts (P < 0.01). The CRC was increased in LP heart mitochondria (P < 0.01). Caspase-3 activity, cytochrome c release, and MDA production were reduced in LP hearts (P < 0.001 and P < 0.01). This study demonstrated that low-pressure reperfusion after hypothermic heart ischemia improves postischemic contractile dysfunction and attenuates necrosis and apoptosis. This protection could be related to an inhibition of mitochondrial permeability transition.

Importance of endothelial nitric oxide synthase for the hypothermic protection of lungs against ischemia-reperfusion injury

OBJECTIVES

The hypothesis that the protective effects of mild hypothermia against the pulmonary ischemia-reperfusion injury are mediated by endothelial nitric oxide synthase was tested.

METHODS

Endothelial nitric oxide synthase knock-out and wild-type mice were sham operated or underwent a 1-hour occlusion of the left pulmonary hilum, followed by 5 hours of reperfusion. Temperature in the left pleural cavity during ischemia was maintained at either 36 degrees C (normothermia) or 32 degrees C (hypothermia). Inflammatory response (myeloperoxidase activity), endothelial barrier function (extravasation of Evans blue-labeled albumin), and endothelial nitric oxide synthase expression and phosphorylation were determined at the end of reperfusion.

RESULTS

After normothermic ischemia both strains had a similar mortality (wild-type, 22.9%; knock-out, 15.4%), which was completely abolished by hypothermia. Endothelial barrier function was disturbed after normothermic ischemia in both wild-type and knock-out mice. Mild hypothermia significantly reduced pulmonary Evans blue extravasation in wild-type mice, but not in knock-out mice. Myeloperoxidase activity increased after normothermic ischemia to the same degree in both strains. This response was significantly attenuated by hypothermia in wild-type mice, but not in knock-out mice. In wild-type mice, endothelial nitric oxide synthase expression and phosphorylation were higher after hypothermic ischemia than after normothermic ischemia. No effect of ischemia on expression of inducible nitric oxide synthase was found in wild-type or knock-out mice.

CONCLUSION

Hypothermic protection against pulmonary ischemia-reperfusion injury is dependent on endothelial nitric oxide synthase and is associated with increased expression and phosphorylation of endothelial nitric oxide synthase.

Cholestatic liver disease modulates susceptibility to ischemia/reperfusion-induced arrhythmia, but not necrosis and hemodynamic instability: the role of endogenous opioid peptides

BACKGROUND/AIMS

Acute cholestasis is associated with cardiovascular complications, which mainly manifest during stressful conditions. The goal of this study is to evaluate susceptibility of 7-day bile duct-ligated rats to ischemia/reperfusion-induced injury.

METHODS

Sham-operated and cholestatic rats, treated with daily normal saline, L-NAME (a non-selective NO synthase inhibitor) naltrexone, or both L-NAME and naltrexone were subjected to 30 min of ischemia followed by 2 h of reperfusion.

RESULTS

Cholestatic rats demonstrated significant bradycardia, hypotension (P < 0.01), and QT prolongation (P < 0.001). The incidence of premature ventricular contractions (P < 0.01), incidence and duration of ventricular tachycardia (P < 0.05), but not ventricular fibrillation, were significantly lower in cholestatic rats. There was no significant difference in hemodynamic instability and infarct size between the groups. L-NAME corrected QT prolongation in cholestatic rats (P < 0.05), with no effect on heart rate, blood pressure and arrhythmia. Naltrexone restored normal heart rate (P < 0.05), blood pressure (P < 0.05) and susceptibility to arrhythmia (P < 0.05) in cholestatic animals, with no significant effect on QT interval. L-NAME and naltrexone co-administration corrected bradycardia (P < 0.05), hypotension (P < 0.05), QT prolongation (P < 0.05) and abolished resistance of cholestatic rats against arrhythmia (P < 0.05).

CONCLUSIONS

This study suggests that short-term cholestasis is associated with resistance against ischemia/reperfusion-induced arrhythmia, which depends on availability of endogenous opioids.

Efficiency of L-arginine enriched cardioplegia and non-cardioplegic reperfusion in ischemic hearts

OBJECTIVE

Endothelial dysfunction with decreased nitric oxide (NO) levels has been implicated on reperfusion injury. Although L-arginine has been shown to diminish reperfusion injury in in vitro studies, clinical studies were very limited.

METHODS

Forty patients with acute myocardial ischemia undergoing CABG were randomized to a study and a control group. L-Arginine was added to cardioplegia solutions in study group. A non-cardioplegic warm blood solution with 8 mmol/l L-arginine infused for controlled reperfusion. Control patients received same protocol without L-arginine. Myocardial O2, lactate, nitrite and malondialdehyde extractions were measured in addition to calculation of CK-MB/CPK ratio and hemodynamic data.

RESULTS

While there was no mortality in study group, one patient in control group died. Overall and nitrite (P=0.01) and lactate extractions (P=0.04) was higher in study and control groups, respectively. Myocardial O2 uptake was higher and malondialdehyde extraction was lower in study group. CK-MB/CPK ratio at postoperative sixth hour was also significantly lower in study group. Ninety percent of the study group had spontaneous return of the sinus rhythm, while 80% of the control patients required defibrillation (P<0.0001). In addition to significantly better hemodynamics, perioperative myocardial infarction incidence was lower (P=0.037), the length of intensive care unit (P=0.009) and hospital (0.014) stays were shorter in study group.

CONCLUSIONS

Use of L-arginine for protection of acutely ischemic myocardium appears to be a safe technique. L-Arginine supplementation increased NO levels and attenuated free O2 radical mediated myocardial injury. Controlled reperfusion with l-arginine enriched non-cardioplegic blood could be a new therapeutic entity to diminish ischemia/reperfusion injury.

Statins and the response to myocardial injury

The benefits of long-term statin (HMG-CoA reductase inhibitor) treatment for preventing coronary events have been well documented in several large-scale prospective clinical trials. By influencing the determinants of myocardial injury, statins may produce direct cardioprotective effects in the ischemic myocardium and prevent further damaging recurrent events. Although not proven fully in a clinical setting, cholesterol-independent or 'pleiotropic' effects of statins are thought to protect against myocardial injury and may occur via a number of mechanisms. Endothelial dysfunction occurs early in the development of atherosclerosis and is associated with a reduction in endothelial nitric oxide (NO) production. Statins have been shown to increase the expression of endothelial NO synthase, with subsequent augmentation of NO in the vasculature. Statins have also been reported to have anti-inflammatory effects, reducing the release of cytokines and chemokines, decreasing the expression of pro-inflammatory cell adhesion molecules, and reducing the accumulation of neutrophils in myocardial tissue following ischemia and reperfusion. Indeed, the role of statins in reducing infarct size is supported by data from a number of preclinical studies. Statin treatment, administered at the onset of reperfusion, has been shown to reduce infarct size by approximately 50% following ischemia in various animal models, and this may be an NO-dependent effect. Randomized clinical trials have indicated that early initiation of statin treatment is associated with a reduction in both the rate of recurrence of cardiovascular events and death in patients with acute coronary syndrome. In addition, decreased rates of myocardial infarction and mortality were demonstrated in several retrospective studies where statin treatment was administered before an interventional procedure. There is a need for further clinical trials to fully elucidate the importance of pre-procedural statin therapy and to determine the extent and mechanisms by which statins exert their cardioprotective effects.

KATP channel activation induces ischemic preconditioning of the endothelium in humans in vivo

BACKGROUND

Endothelial dysfunction contributes to ischemia-reperfusion injury (IRI) and is reduced by ischemic preconditioning (IPC). IPC may involve activation of ATP-sensitive potassium channels (K(ATP)). We determined whether modulation of K(ATP) channels occurs in endothelial IPC in humans.

METHODS AND RESULTS

IRI of the forearm was induced by inflating a blood pressure cuff to 200 mm Hg for 20 minutes in healthy volunteers. K(ATP) activation was modulated by intra-arterial glibenclamide (blocker) and diazoxide (opener). Endothelial function (response to intra-arterial acetylcholine) was assessed with forearm plethysmography before and after (1) 15-minute reperfusion, (2) IRI preceded by IPC (3 five-minute periods of ischemia), (3) IRI preceded by IPC with glibenclamide, (4) IPC followed by glibenclamide before IRI, (5) IRI preceded by diazoxide, and (6) IRI preceded by coinfusion of glibenclamide with diazoxide. IRI caused endothelial dysfunction (P=0.002), which IPC prevented (P=0.40). Glibenclamide abolished IPC when given contemporaneously with (P=0.003) or during IRI (P=0.0005). Diazoxide prevented endothelial dysfunction after IRI (P=0.68) but not when coinfused with glibenclamide.

CONCLUSIONS

Glibenclamide abolishes and diazoxide mimics endothelial IPC in humans. The time course of the effect of glibenclamide suggests involvement of K(ATP) channels as effectors of endothelial IPC in vivo. These data may have implications for understanding the therapeutic role of agents that modulate K(ATP) channel function.

Protective effect of N-acetylcysteine against oxygen radical-mediated coronary artery injury

The present study investigated the protective effect of N-acetylcysteine (NAC) against oxygen radical-mediated coronary artery injury. Vascular contraction and relaxation were determined in canine coronary arteries immersed in Kreb's solution (95% O2-5% CO2), incubated or not with NAC (10 mM), and exposed to free radicals (FR) generated by xanthine oxidase (100 mU/ml) plus xanthine (0.1 mM). Rings not exposed to FR or NAC were used as controls. The arteries were contracted with 2.5 microM prostaglandin F2alpha. Subsequently, concentration-response curves for acetylcholine, calcium ionophore and sodium fluoride were obtained in the presence of 20 microM indomethacin. Concentration-response curves for bradykinin, calcium ionophore, sodium nitroprusside, and pinacidil were obtained in the presence of indomethacin plus Nomega-nitro-L-arginine (0.2 mM). The oxidative stress reduced the vascular contraction of arteries not exposed to NAC (3.93 +/- 3.42 g), compared to control (8.56 +/- 3.16 g) and to NAC group (9.07 +/- 4.0 g). Additionally, in arteries not exposed to NAC the endothelium-dependent nitric oxide (NO)-dependent relaxation promoted by acetylcholine (1 nM to 10 microM) was also reduced (maximal relaxation of 52.1 +/- 43.2%), compared to control (100%) and NAC group (97.0 +/- 4.3%), as well as the NO/cyclooxygenase-independent receptor-dependent relaxation provoked by bradykinin (1 nM to 10 microM; maximal relaxation of 20.0 +/- 21.2%), compared to control (100%) and NAC group (70.8 +/- 20.0%). The endothelium-independent relaxation elicited by sodium nitroprusside (1 nM to 1 microM) and pinacidil (1 nM to 10 microM) was not affected. In conclusion, the vascular dysfunction caused by the oxidative stress, expressed as reduction of the endothelium-dependent relaxation and of the vascular smooth muscle contraction, was prevented by NAC.

ISCHAEMIA ENHANCES THE ROLE OF CA2+-ACTIVATED K+ CHANNELS IN ENDOTHELIUM-DEPENDENT AND NITRIC OXIDE-MEDIATED DILATATION OF THE RAT HINDQUARTERS VASCULATURE

1. We compared the effects of the nitric oxide synthase inhibitor N(G)-nitro-L-arginine (L-NOARG) and tetraethylammonium (TEA), a blocker of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels, on vasodilator responses to endothelium-dependent (acetylcholine; ACh) and -independent (sodium nitroprusside; SNP) vasodilators. The mechanism of the vasodilator responses was determined in rat hindquarters under normal conditions (sham ischaemia) and after 2 h ischaemia followed by reperfusion with physiological saline. 2. In sham ischaemia, the responses to ACh were significantly reduced by L-NOARG (1 mmol/L) and TEA (1 mmol/L) and there was a further reduction in response the presence of both agents. Dilator responses to SNP were significantly enhanced by L-NOARG, whereas TEA did not alter the SNP-induced vasodilatation when given either alone or in the presence of L-NOARG. 3. After ischaemia, L-NOARG caused a similar inhibition of ACh-induced dilatation to that observed in sham ischaemia. However, TEA alone or combined with L-NOARG caused a significantly greater inhibition of the ACh-induced vasodilatation after ischaemia than observed in the sham ischaemia group. Tetraethylammonium alone did not affect the responses to SNP, but it did attenuate the enhanced dilatation observed in the presence of L-NOARG. 4. In the rat hindquarters vasculature, both nitric oxide and the opening of TEA-sensitive K(+) channels contribute to ACh-induced endothelium-dependent dilatation. In addition, a TEA-sensitive mechanism was not involved in the SNP-induced dilatation under normal conditions but, after ischaemia, if there is a further inhibition of endogenous nitric oxide by L-NOARG, exogenous nitric oxide causes dilatation that is sensitive, in part, to TEA. Thus, the contribution of the opening of BK(Ca) channels to endothelium-dependent vasodilatation assumes greater importance after ischaemia and reperfusion. This may reflect an increased ability of nitric oxide or cGMP to open BK(Ca) channels after ischaemia.

Antioxidative, antinitrative, and vasculoprotective effects of a peroxisome proliferator-activated receptor-gamma agonist in hypercholesterolemia

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR) signaling pathways have been reported to exert anti-inflammatory effects and attenuate atherosclerosis formation. However, the mechanisms responsible for their anti-inflammatory and antiatherosclerotic effects remain largely unknown. The present study tested the hypothesis that a PPARgamma agonist may exert significant endothelial protection by antioxidative and antinitrative effects.

METHODS AND RESULTS

Male New Zealand White rabbits were randomized to receive a normal (control) or a high-cholesterol diet and treated with vehicle or rosiglitazone (a PPARgamma agonist) 3 mg x kg(-1) x d(-1) for 5 weeks beginning 3 weeks after the high-cholesterol diet. At the end of 8 weeks of a high-cholesterol diet, the rabbits were killed, and the carotid arteries were isolated. Bioactive nitric oxide was determined functionally (endothelium-dependent vasodilatation) and biochemically (the phosphorylation of vasodilator-stimulated phosphoprotein, or P-VASP). Vascular superoxide production, PPARgamma, gp91phox, and inducible nitric oxide synthase (iNOS) expression, and vascular ONOO- formation were determined. Hypercholesterolemia caused severe endothelial dysfunction and reduced P-VASP, despite a marked increase in iNOS expression and total NOx production. Treatment with rosiglitazone enhanced PPARgamma expression, improved endothelium-dependent vasodilatation, preserved P-VASP, suppressed gp91phox and iNOS expression, reduced superoxide and total NOx production, and inhibited nitrotyrosine formation.

CONCLUSIONS

The PPARgamma agonist rosiglitazone exerted a significant vascular protective effect in hypercholesterolemic rabbits, most likely by attenuation of oxidative and nitrative stresses. The endothelial protective effects of PPARgamma agonists may reduce leukocyte accumulation in vascular walls and contribute to their antiatherosclerotic effect.

Reduction of myocardial infarct size by fluvastatin

Statins have a variety of cardioprotective properties following chronic treatment. In contrast, little is known about the acute effects. Reperfusion acutely injures the heart by activation of neutrophils as well as endothelial cells. Because statins are known to influence the processes pathogenetically involved, we hypothesized that acute application of statins attenuates the sequelae of cardiac reperfusion. In rats, myocardial infarction (MI) was induced by ligature of the left coronary artery followed by reperfusion. Myocardial blood flow (MBF) was determined by H2 clearance and regional myocardial function (fractional thickening, FT) by pulsed Doppler. MI size was measured by triphenyltetrazolium chloride (TTC) staining, neutrophil extravasation by determination of myeloperoxidase (MPO) activity, and nitric oxide generation via measurement of cGMP. Treatment with fluvastatin, administered intravenously 20 min before the onset of ischemia, significantly attenuated the decline of FT and MBF at the end of the reperfusion period and significantly reduced MI size. Furthermore, fluvastatin induced a significant reduction of MPO activity and an increase of cGMP level compared with the control group. The effect of fluvastatin was completely abolished following pretreatment of NG-nitro-l-arginine methyl ester (l-NAME). These findings suggest that acute application of fluvastatin reduces MI size and attenuates reperfusion injury. We propose that the underlying mechanism is at least partially an inhibition of inflammation and endothelial dysfunction by preventing the activation and extravasation of neutrophils.

Transient limb ischemia induces remote ischemic preconditioning in vivo

BACKGROUND

Ischemic preconditioning reduces local tissue injury caused by subsequent ischemia-reperfusion (IR), but may also have a salutary effect on IR injury of tissues remote from those undergoing preconditioning. We tested the hypothesis that limb ischemia induces remote preconditioning, reduces endothelial IR injury in humans, and reduces experimental myocardial infarct size.

METHODS AND RESULTS

Endothelial IR injury of the human forearm was induced by 20 minutes of upper limb ischemia (inflation of a blood pressure cuff to 200 mm Hg) followed by reperfusion. Remote preconditioning was induced by three 5-minute cycles of ischemia of the contralateral limb. Venous occlusion plethysmography was used to assess forearm blood flow in response to acetylcholine at baseline and 15 minutes after reperfusion. Experimental myocardial infarction was achieved by 40 minutes of balloon occlusion of the left anterior descending artery in 15-kg pigs. Remote preconditioning was induced by four 5-minute cycles of lower limb ischemia. Triphenyltetrazolium staining was used to assess the extent of myocardial infarction. In the human study, the response to acetylcholine was significantly attenuated in the control group after 15 minutes' reperfusion, but remote preconditioning prevented this reduction. Limb ischemia caused a significant reduction in the extent of myocardial infarction relative to the area at risk compared with control (26+/-9% versus 53+/-8%, P<0.05).

CONCLUSION

Remote ischemic preconditioning prevents IR-induced endothelial dysfunction in humans and reduces the extent of myocardial infarction in experimental animals. Transient limb ischemia is a simple preconditioning stimulus with important potential clinical applications.

Role of ceramide in TNF-alpha-induced impairment of endothelium-dependent vasorelaxation in coronary arteries

The present study tested the hypothesis that ceramide, a sphingomylinase metabolite, serves as an second messenger for tumor necrosis factor-alpha (TNF-alpha) to stimulate superoxide production, thereby decreasing endothelium-dependent vasorelaxation in coronary arteries. In isolated bovine small coronary arteries, TNF-alpha (1 ng/ml) markedly attenuated vasodilator responses to bradykinin and A-23187. In the presence of N(G)-nitro-L-arginine methyl ester, TNF-alpha produced no further inhibition on the vasorelaxation induced by these vasodilators. With the use of 4,5-diaminofluorescein diacetate fluorescence imaging analysis, bradykinin was found to increase nitric oxide (NO) concentrations in the endothelium of isolated bovine small coronary arteries, which was inhibited by TNF-alpha. Pretreatment of the arteries with desipramine (10 microM), an inhibitor of acidic sphingomyelinase, tiron (1 mM), a superoxide scavenger, and polyethylene glycol-superoxide dismutase (100 U/ml) largely restored the inhibitory effect of TNF-alpha on bradykinin- and A-23187-induced vasorelaxation. In addition, TNF-alpha activated acidic sphingomyelinase and increased ceramide levels in coronary endothelial cells. We conclude that TNF-alpha inhibits NO-mediated endothelium-dependent vasorelaxation in small coronary arteries via sphingomyelinase activation and consequent superoxide production in endothelial cells.

Nitric oxide inhalation prompts weaning from the right ventricular assist device: evaluation under continuous-flow biventricular assistance

OBJECTIVE

The objective of this study was to investigate the effect of nitric oxide on the recovery of right heart function under global ischemia with a continuous-flow biventricular assist device support.

METHODS

Fifteen piglets were divided into three groups: continuous-flow biventricular assist support only (control group), global ischemia with continuous-flow biventricular assist support (ischemia only group), and global ischemia with continuous-flow biventricular assist support plus nitric oxide inhalation (nitric oxide group). Two continuous-flow pumps were used as left and right ventricular assist devices. In the ischemic groups (ischemia only group and nitric oxide group), global ischemia was induced for 30 minutes and followed by a 6-hour reperfusion period; the nonischemic control group underwent a 6-hour perfusion period only. The left ventricular assist device was driven at a flow rate of more than 75 to 80 mL/(min. kg). The right ventricular assist device was driven so as to sustain the left ventricular assist device flow, and the animal was weaned from it in accordance with the objective of cardiac recovery.

RESULTS

Mean pulmonary arterial pressure remained low in the nitric oxide group (mean 23 mm Hg), whereas it rose from 19.9 mm Hg to 39.3 mm Hg in the ischemia group and to 26.2 mm Hg in the control group. Mixed venous saturation was maintained at more than 60% in all cases. Although no piglets in the ischemia group were able to survive without continuous-flow biventricular assist support, the right ventricular assist device flow ratio (device flow/total systemic flow) in the nitric oxide group could be reduced in all cases, and it was possible to wean the piglets from right ventricular assist device support in 4 of 5 cases.

CONCLUSION

Inhalation of 40-ppm nitric oxide enabled smoother maintenance of the left ventricular assist device flow and prompted the weaning from right ventricular assist device support on continuous-flow biventricular assist.

Effects of homocysteine on intracellular nitric oxide and superoxide levels in the renal arterial endothelium

The present study was designed to test the hypothesis that homocysteine (Hcys) reduces intracellular nitric oxide (NO) concentrations ([NO](i)) and stimulates superoxide (O.) production in the renal arterial endothelium, thereby resulting in endothelial dysfunction. With the use of fluorescence microscopic imaging analysis, a calcium ionophore, A-23187 (2 microM), and bradykinin (2 microM) were found to increase endothelial [NO](i) in freshly dissected lumen-opened small renal arteries loaded with 4,5-diaminofluorescein diacetate (DAF-2DA; 10 microM). Preincubation of the arteries with L-Hcys (20-40 microM) significantly attenuated the increase in endothelial [NO](i). However, L-Hcys had no effect on NO synthase activity in the renal arteries, as measured by the conversion rate of [(3)H]arginine to [(3)H]citrulline, but it concentration dependently decreased DAF-2DA-sensitive fluorescence induced by PAPA-NONOate in the solution, suggesting that L-Hcys reduces endothelial [NO](i) by its scavenging action. Because other thiol compounds such as L-cysteine and glutathione were also found to reduce [NO](i), it seems that decreased NO is not the only mechanism resulting in endothelial dysfunction or arteriosclerosis in hyperhomocysteinemia (hHcys). By analysis of intracellular O. levels using dihydroethidium trapping, we found that only L-Hcys among the thiol compounds studied markedly increased O. levels in the renal endothelium. These results indicate that L-Hcys inhibits the agonist-induced NO increase but stimulates O. production within endothelial cells. These effects of L-Hcys on [NO](i) and [O.] may contribute to endothelial injury associated with hHcys.

Pharmacological approaches to preserving and restoring coronary endothelial function

There is compelling evidence that the endothelium is critical to normal coronary vascular function and that endothelial dysfunction, generally indicated by an impairment of endothelium-dependent vasodilatation, is an important component of coronary artery disease (CAD). Endothelial cells synthesise and release a number of factors, including prostacyclin, nitric oxide (NO), endothelium-derived hyperpolarising factor (EDHF) and endothelin, which are important in the regulation of vascular tone and the control of platelet and leukocyte adhesion, aggregation and migration. NO appears to be the critical factor in the preservation of normal coronary vascular function and there is a well-established correlation between CAD and an impairment of NO activity. Thus, to preserve endothelial function, drugs have been used to either increase the synthesis of NO, or to decrease its breakdown. Fortuitously, compounds such as the HMG-CoA reductase inhibitors, angiotensin (AT) converting enzyme inhibitors (ACEIs), AT receptor antagonists and oestrogen, which have been introduced into clinical practice because of other beneficial effects, have also been shown to improve coronary endothelial function through a variety of mechanisms. In addition, L -arginine, the substrate for NO synthesis, and the anti-oxidants ascorbate and alpha-tocopherol, are able to increase NO synthesis and bioavailability respectively. Studies in experimental animals strongly support the ability of these agents to enhance the activity of endothelium-derived NO but clinical trials have failed to demonstrate reversal of established CAD. Whether these agents preserve endothelial function and prevent the development of CAD remains to be established.

Protective effects of FK409, a novel nitric oxide donor, against postischemic myocardial dysfunction in guinea-pig hearts

Effects of FK409 were investigated in perfused guinea-pig Langendorff hearts subjected to ischemia and reperfusion. Nitric oxide electrode, fluorometry, and 31P nuclear magnetic resonance imaging were used to monitor changes in cellular high-phosphorous energy and nitric oxide and Ca2+ content in the heart together with simultaneous recordings of left ventricular developed pressure. After cardioplegic arrest with St. Thomas' Hospital solution, normothermic (37 degrees C) global ischemia was induced for 40 min, and hearts were reperfused for 40 min. FK409 at 10(-8) M, which has a minimum inotropic effect on nonischemic hearts, was added to the cardioplegic solution. Treatment with FK409 reduced left ventricular developed pressure during and after ischemia and improved postischemic recovery of left ventricular developed pressure from 55.4% at 40 min of reperfusion in FK409-free hearts up to 80.4% in hearts treated with FK409 (p < 0.01). Flow rate at 1.5 min after treatment with the cardioplegic solution was 27.7 ml/min in hearts treated with FK409 compared with 21.2 ml/min in drug-free hearts (p < 0.01). Treatment with FK409 significantly effected preservation of tissue level of beta-adenosine triphosphate at the end of ischemia or reperfusion. During ischemia, arrested with the cardioplegic solution, intracellular Ca2+ accumulation and nitric oxide release were reduced. At the end of ischemia in FK409-treated hearts, nitric oxide release was 86% greater than in drug-free hearts without reference to the Ca2+ concentration. In cardiac surgery, normothermic arrested hearts are subject to damage by oxygen free radicals in reperfusion injury. Therefore, nitric oxide exogenously supplied by FK409 was responsible for the cardioprotective action, presumably by acting directly as an oxygen radical scavenger during reperfusion. A specific nitric oxide donor, like FK409, may have therapeutic use as a nitric oxide-mediated vasorelaxant and additional protective action for reperfusion-injury hearts.

Endothelial dysfunction is induced by proinflammatory oxidant hypochlorous acid

The myeloperoxidase (MPO)-derived oxidant hypochlorous acid (HOCl) plays a role in tissue injury under inflammatory conditions. The present study tests the hypothesis that HOCl decreases nitric oxide (NO) bioavailability in the vasculature of Sprague-Dawley rats. Aortic ring segments were pretreated with HOCl (1-50 microM) followed by extensive washing. Endothelium-dependent relaxation was then assessed by cumulative addition of acetylcholine (ACh) or the calcium ionophore A23187. HOCl treatment significantly impaired both ACh- and A23187-mediated relaxation. In contrast, endothelium-independent relaxation induced by sodium nitroprusside was unaffected. The inhibitory effect of HOCl on ACh-induced relaxation was reversed by exposure of ring segments to L-arginine but not D-arginine. In cellular studies, HOCl did not alter endothelial NO synthase (NOS III) protein or activity, but inhibited formation of the NO metabolites nitrate (NO3(-) and nitrite (NO2(-). The reduction in total NO metabolite production in bovine aortic endothelial cells was also reversed by addition of L-arginine. These data suggest that HOCl induces endothelial dysfunction via modification of L-arginine.

Role of nitric oxide and protein kinase C in ACh-induced cardioprotection

We examined the roles of nitric oxide and protein kinase C (PKC) in ACh-produced protection of cultured cardiomyocytes during simulated ischemia and reoxygenation. Cell viability was quantified using propidium iodide in chick embryonic ventricular myocytes. O(2) radicals were quantified using 2',7'-dichlorofluorescin diacetate. After a 10-min infusion of ACh (0.5 or 1 mM) and a 10-min drug-free period, we simulated ischemia for 1 h and reoxygenation for 3 h. ACh reduced cardiocyte death [32 +/- 4%; n = 6 and 23 +/- 4%; n = 7 (P < 0.05)] and attenuated oxidant stress during ischemia and reoxygenation in a concentration-dependent manner compared with controls (47 +/- 4%; n = 8; P < 0.05). The increase in O(2) radicals before simulated ischemia [357 +/- 49; n = 4 and 528 +/- 52; n = 8 vs. 211 +/- 34; n = 8; P < 0.05 (arbitrary units)] was abolished by the specific nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) and was markedly attenuated by N(G)-monomethyl-L-arginine (L-NMMA). L-NAME or L-NMMA blocked the protective effects of ACh, which selectively increased PKC-epsilon isoform activity in the particulate fraction. The PKC inhibitor Gö-6976 had no effect on O(2) radical production before simulated ischemia but it abolished the protection; therefore nitric oxide is a large component of ACh-generated O(2) radicals. Nitric oxide and O(2) radicals activate the PKC-epsilon isoform by which ACh protects against injury.

L-arginine chlorination products inhibit endothelial nitric oxide production

The myeloperoxidase-derived oxidant hypochlorous acid (HOCl) is thought to contribute to endothelial dysfunction, but the mechanisms underlying this inhibitory effect are unknown. The present study tested the hypothesis that HOCl and L-arginine (L-Arg) react to form novel compounds that adversely affect endothelial function by inhibiting nitric oxide (NO) formation. Using spectrophotometric techniques, we found that HOCl and L-Arg react rapidly (k = 7.1 x 10(5) m(-1) s(-1)) to form two major products that were identified by mass spectrometry as monochlorinated and dichlorinated adducts of L-Arg. Pretreatment of bovine aortic endothelial cells with the chlorinated L-Arg metabolites (Cl-l-Arg) inhibited the -induced formation of the NO metabolites nitrate (NO(3)(-)) and nitrite (NO(2)(-)) in a concentration-dependent manner. Preincubation of rat aortic ring segments with Cl-L-Arg resulted in concentration-dependent inhibition of acetylcholine-induced relaxation. In contrast, blood vessels relaxed normally to the endothelium-independent vasodilator sodium nitroprusside. In vivo administration of Cl-L-Arg to anesthetized rats increased carotid artery vascular resistance. A greater than 10-fold excess of L-Arg was required to reverse the inhibitory effects of Cl-L-Arg in vivo and in vitro. Reaction of HOCl with D-arginine (D-Arg) did not result in the formation of inhibitory products. These results suggest that HOCl reacts with L-Arg to form chlorinated products that act as nitric-oxide synthase inhibitors.

Ceramide reduces endothelium-dependent vasodilation by increasing superoxide production in small bovine coronary arteries

Ceramide serves as a second messenger in a variety of mammalian cells. Little is known regarding the role of ceramide in the regulation of vascular endothelial function. The present study was designed to determine whether ceramide affects endothelium-dependent vasodilation in coronary arteries and to explore the mechanism of action of ceramide. In isolated and pressurized small bovine coronary arteries, cell-permeable C(2)-ceramide (10(-)(5) mol/L) markedly attenuated vasodilator responses to bradykinin and A23187 (by 40% and 60%, respectively). In the presence of K(G)-nitro-L-arginine methyl ester, ceramide produced no further inhibition on the vasodilation induced by these vasodilators. Ceramide had no effect on DETA NONOate-induced vasodilation. By use of a fluorescence NO indicator (4,5-diaminofluorescein diacetate), intracellular NO was measured in the endothelium of freshly isolated small coronary arteries. It was found that ceramide significantly inhibited bradykinin-induced NO increase within endothelial cells. However, it had no effect on the activity of arterial or endothelial NO synthase. Pretreatment of the arteries with sodium dihydroxybenzene disulfonate (Tiron, 10(-)(3) mol/L), a cell-permeable superoxide scavenger, or polyethylene glycol superoxide dismutase (100 U/mL) largely restored the inhibitory effects of ceramide on the vasodilation and NO increase induced by bradykinin or A23187. Moreover, ceramide time-dependently increased intracellular superoxide (O(2)(-. )) in the endothelium, as measured by a fluorescent O(2)(-. )indicator, dihydroethidium. These results demonstrate that ceramide inhibits endothelium-dependent vasodilation in small coronary arteries by decreasing NO in vascular endothelial cells and that this decrease in NO is associated with increased O(2)(-. ) but not with the inhibition of NO synthase activity within these cells.

Ischemic preconditioning prevents endothelial injury and systemic neutrophil activation during ischemia-reperfusion in humans in vivo

BACKGROUND

Endothelial dysfunction leading to neutrophil infiltration of tissues has been implicated in tissue injury caused by ischemia-reperfusion (IR). Tissue injury during IR can be reduced by prior ischemic preconditioning (IPC). In humans, it is unclear whether endothelial dysfunction occurs during IR or whether IPC offers protection against endothelial dysfunction and inflammatory cell activation. We studied the effects of experimental IR on endothelial and neutrophil function in the human forearm in vivo and examined the protection afforded by IPC.

METHOD AND RESULTS

The forearm was made ischemic for 20 minutes by inflating a blood pressure cuff to 200 mm Hg. We assessed endothelial function of conduit (radial artery flow-mediated dilation) and resistance vessels (blood flow responses to intra-arterial infusion of the endothelium-dependent dilator acetylcholine) in healthy volunteers before and after IR. IR reduced flow-mediated dilation of the radial artery at 15 minutes of reperfusion (7.7+/-1.5% to 3.5+/-0.9%) and the dilator response of resistance vessels to acetylcholine at 15, 30, and 60 minutes of reperfusion. IR did not reduce the dilator response of the radial artery to glyceryltrinitrate and only caused a small reduction of glyceryltrinitrate-induced dilation of resistance vessels at 60 minutes of reperfusion. IR caused an increase in neutrophil CD11b expression and platelet-neutrophil complexes in the circulating blood. IPC (three 5-minute episodes of ischemia) before IR prevented endothelial dysfunction and neutrophil activation.

CONCLUSIONS

A clinically relevant period of ischemia-reperfusion causes profound and sustained endothelial dysfunction and systemic neutrophil activation. IPC attenuates both of these effects in humans.